The present invention relates to a direct bonding method for bonding a III-V group compound semiconductor layer on a silicon substrate.
Recently, attention to a direct bonding method for of a III-V group compound semiconductor layer such as an InP layer on a silicon substrate has been on the increase in place of the heteroepitaxial growth. The heteroepitaxial growth has disadvantages in large lattice mismatch causing at high density crystal defects such as threading dislocations and in a large difference in thermal expansion coefficients which may provide a large thermal stress. The direct bonding method has been developed to prevent the above disadvantages of the heteroepitaxial growth, but the following serious problems still remain.
The bonding of the III-V group compound semiconductor layer requires a heat treatment at a relatively high temperature to cause atomic re-arrangements on a bonding interface for secure bonding. This high temperature heat treatment and subsequent cooling stage may raise other serious problems. The III-V group compound semiconductor layer has a large difference in thermal expansion from the silicon substrate. The heat treatment for bonding the III-V group compound semiconductor layer on the silicon substrate and subsequent cooling stage thereof may introduce a large thermal stress due to the difference in the thermal expansion coefficient between the III-V group compound semiconductor and the silicon substrate. The thermal stress may introduce various crystal defects such as dislocations into mainly the III-V group compound semiconductor layer acting as a device layer. The III-V group compound semiconductor layer having many crystal defects such as dislocations, particularly threading dislocations is not usable. If a low temperature heat treatment is carried out for bonding the III-V group compound semiconductor layer on the silicon substrate, it is difficult to obtain a necessary large bonding intensity.
It has been required to provide a novel method of bonding III-V group compound semiconductor layer on the silicon layer free from introduction of any crystal defects such as dislocations but is able to obtain a strong bonding intensity.